ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    , Volume 33 Issue 7 Previous Issue    Next Issue
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    THEORETICAL RESEARCH OF TRANSITION FROM DENDRITE TO FINE CELL IN SUB-RAPID SOLIDIFICATION
    GENG Xingguo; FU Hengzhi(Northwestern Polytechnical University; Xi'an 710072) (International Centre .for Materials Physics; Chinese Academy of Sciences;Shenyang 110015)
    Acta Metall Sin, 1997, 33 (7): 673-676. 
    Abstract   PDF (366KB) ( 554 )
    From the stability of the cylindrical interface, a criterion of the transition from dendrite to fine cell in sub-rapid solidification has been constructed. The calculated results agree well with the experimental results for Al-Mn alloy.
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    MORPHOLOGIES OF (Al,Ag)_3Ti AND Ti_3AlC PRECIPITATES IN Ll_0-TiAl INTERMETALLIC COMPOUND
    TIAN Wenhuai;YANG Haichun (Universily of Science and Technology Beijing; Beij ing 100083); NEMOTO Minoru (Kyushu University; Japan)
    Acta Metall Sin, 1997, 33 (7): 677-682. 
    Abstract   PDF (1630KB) ( 572 )
    A trasmission electron microscopy (TEM) investigation has been performed on the moerphologies of Ll2-(Al,Ag),Ti and Ti3AIC precipitates in Ll0-ordered TiAl(Ag). During aging at temperatures around 1073 K after quenching from 1473 K, TiAl(Ag) hardens by the precipitation of (Al,Ag)3Ti and Ti3AIC. TEM observations revealed that plate-like precipitates (Al,Ag)3Ti lie on (001) plane of TiAl(Ag) matrix and needle--like pricipitates Ti3AlC, which lie only in one direction parallel to the [001] axis of the TiAl(Ag) matrix, appear after longer period aging or higher temperature aging. The anisotropic misfits between TiAl matrix and Ll2-(Al,Ag)3Ti and Ti3AIC can be considered to explain the morphologies of (Ag,Al)3Ti and Ti3AIC precipitates.
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    MICROSTRUCTURE CHARACTERISTICS OF A HIGH DUCTILITY γ-TiAL ALLOY
    CHEN Xiaoqun;HUANG Baiyun;HE Yuehui;QU Xuanhui (Central South University of Technology; Changrha 410083); LEI Changhui (Beting Laboratory o.f Electron Microscopy; Chinese Academy of Sciences; Beijing 100080)
    Acta Metall Sin, 1997, 33 (7): 683-689. 
    Abstract   PDF (3220KB) ( 735 )
    The microstructure and mechanical properties of a titanium aluminide alloy, Ti-33Al-3Cr-0.5Mo, under a multi-step thermo-mechanical treatment were studied. A sub-duplex microstructure with fine equiaxial y grains as the major phase and β2, α2 as the minor phases was obtained after final heat treatment at 1250℃, for 4h+controlled cooling.Tensile elongation for the alloy can reach 5.07% at room temperature. The principal reasons for disproving elongation are the refine of grain and improvment of grain boundary structure.
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    MECHANISMS OF COMPATIBLE PLASTIC DEFORMATION BETWEEN THE γ-LAMELLAE IN TWO PHASE TiAl-BASE ALLOY
    LIANG Wei;YANG Dezhuang (Harbin institute of Technology; Harbin 150001) (Taiyuan University ofTechnology; Taiyuan 030024)
    Acta Metall Sin, 1997, 33 (7): 690-696. 
    Abstract   PDF (2120KB) ( 605 )
    Mechanisms of compatible plastic deformation in three types of twin-related γ-lamellae have been studied. It was shown that the mechanisms of compatible plastic deformation of both crossing and not crossing lamellar boundary exist in 120°-rotational twin related lamellae. In true twin related lamellae, however, the compatible plastic deformation does not cross the lamellar boundaries. Besides, in pseudo twin related lamellae,the plastic deformation is incompatible.
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    TEM OBSERVATION OF MICROSTRUCTURES AND FINE STRUCTURES DURING BAINITIC NUCLEATION IN THE STEEL 8Mn8SiMo
    WU Xiaolei;CHEN Guangnan (Institute of Mechanics; Chinese Academy of Sciences; Beijing 100080); MA Chaoli;KANG Mokuang (Northwestern Polytechntical University; Xi'an 710072)
    Acta Metall Sin, 1997, 33 (7): 697-701. 
    Abstract   PDF (2166KB) ( 591 )
    The microstructure and substructure of the bainitic-ferrite at the most early stage of growth in an Fe-0.79C-8.3Mn-0.87St-0.50Mo steel are studied by TEM. It is observed that the bainite nuclei exhibit a thin plate morphology. And, the bainite formation has the character of catalysis nucleation by sub-units. Moreover, the existence of (lll)f defect plane is firstly observed, and its formation is considered to be the result of the plastic accommodation effect occurred in parent austenite during bainitic nucleation and growth. Defect planes, in fact, to be the glide plane of austenite matrix, consist of part of the bainitic-ferrite/austenite interface. Thus, the formation of bainitic-ferrite is of shear nature.
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    THE LOW CYCLE FATIGUE BEHAVIOUR FOR 8090 Al-Li ALLOYS
    WU Ximao;Al Suhua;ZHANG Yun;WANG Zhonmang;HAN Xinglin (State Key Laboratory for Fatigue and Fracture of Materials; Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015) (Shenyang Polytechnic University. Shenyang 110023)
    Acta Metall Sin, 1997, 33 (7): 702-708. 
    Abstract   PDF (3251KB) ( 583 )
    Low cycle fatigue property, cyclic hardening and softening of 8090 Al-Li alloys at various aging conditions were studied. The results showed that cyclic response stress in the same aging condition increased with increasing strain amplitude, and aging condition had a little influence on cyclic deformation at low strain amplitude but the influence increased with raising strain amplitude. The characteristics of low cyclic fatigue and cyclic hardening and softening of the alloy were closely related to dislocation morphology, size of precipitate, PFZs along grain boundaries and fracture appearance.
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    IN SITU TEM OBSERVATION OF HYDROGEN-INDUCED CRACKING AND STRESS CORROSION CRACKING FOR Fe_3Al
    GU Biao;NIE Yifan;GAO Kewei;CHU guyana (University of Science and Technology Beijing; Beijing 100083)
    Acta Metall Sin, 1997, 33 (7): 709-717. 
    Abstract   PDF (4151KB) ( 718 )
    The change of dislocation configuration ahead of a loaded crack tip before and after charging with hydrogen, and stress corrosion cracking, and relationship between dislocation and initiation of hydrogen-induced cracking (HIC) for Fe3Al are investigated in TEM using a special constant deflection loading device. The results show that hydrogen can enhance dislocation emission, multiplication and motion, and increase the size of dislocation free zone (DFZ). A nanocrack of HIC will initiate and Dropagae in the DFZ when hydrogen enhanced dislocation emission and motion reach a critical condition. The reasons that hydrogen enhanced dislocation emission and motion, and the mechanism of initiation of HIC have been discussed.
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    APPLICATION-BASIS STUDY OF KEY TECHNOLOGIES IN CARBON-BEARING PELLETS-IRON BATH SMELTING REDUCTION PROCESS
    DU Ting;DU Kun (Central Iron & Steel Research institute; Ministry of Metallurgical Industry; Beijing 100081)
    Acta Metall Sin, 1997, 33 (7): 718-728. 
    Abstract   PDF (1046KB) ( 669 )
    The key technologies in carbon-bearing pellets-iron bath smelting reduction process have been studied systematically, which is based on using non-coke coal and iron concentrate. The experimental research has made a break through in solving problem in high temperature strengh of carbon--bearing pellets, which had not been solved during a long time domestically and abroad. The self-reduction kinetic model of carbon-bearing pellets, reoxidation mechanism and the technical measures for speeding up the prereduction rate and improving the resistant properties against the oxidation of the pellets have been put forward. The new carbon-bearing pellets of high carbon content, high strength, high self-reduction rate and high resistance to oxidation have been developed succesfully. Meanwhile, the melting and reduction kinetics of the pellets in iron bath has been studied. The optimized process parameters of contraling the reduction rate, final reducibility, carbon content in hot metal and desulphurisation have been obtained.
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    EVALUATION AND ANALYSIS OF THE ELECTROCHEMICAL CAPACITY OF METAL HYDRIDE ELECTRODE USING HYDROGEN STORAGE ALLOYS IN ALKALINE AQUEOUS SOLUTION
    JIANG Jianjun (Huazhong University of Science and Technology; Wuhan 430074); LEI YOngquan;SUN Dalin;WU Jing;WANG Qidong (Zhejiang University; Hangzhou 310027)
    Acta Metall Sin, 1997, 33 (7): 729-736. 
    Abstract   PDF (1275KB) ( 420 )
    To determinate an appropriate method measuring the performance of a metal hydride electrode, three different electrochemical apparatus were designed. The results showed that electrochemical capacity of hydride measured by a conventional three-electrode open cell was higher than that determined in a sandwiched and in a sealed Ni/MH test cell.The electrochemical capacity of a hydride electrode measured in a sandwiched Ni/MH cell was very close to that measured in a sealed test cell. In order to optimize the metal hydride electrode alloy and elevalute the discharge capacity of an alloy, the factors affecting the discharge process of an actual hydride electrode were examined theoretically and experimentally. It can be concluded that the electrochemical capacity of a hydride electrode depends not only on the intrinsic properties of a hydrogen storage alloy, but also on the electrode preparation method and its working environment.
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    THE INTERFACIAL ANALYSIS OF MO/SiO_2 MULTILAYERS MIRROR FOR SOFT X-RAY
    WANG Fengping;WANG Peixuan;FANG Zhengzhi (University of Science and Technology Beting; Beting 100083); CUI Mingqi;JIANG Xiaoming; MA Hong; (Institute of High Energy Physics; Chinese Academy of Sciences; Beijing 100039)
    Acta Metall Sin, 1997, 33 (7): 737-741. 
    Abstract   PDF (457KB) ( 467 )
    Groups of Mo/Sio2 multilayer films were fabricated by magnetron sputter ing in Ar atmosphere. Low angle X-ray diffraction analysis of the multilayers was carried out at the diffusion scattering station of BSRF. The interfacial roughness and periodic structure are investigated through simulation of low angle X-ray diffraction spectra based on the dynamical theory. The periodic structure and composition of Mo/SiO2 multilayers were also characterized with AES. The results show that very good composition modulation struc ture formed, and no obvious diffusion of St and / or O through Mo layers is observed.
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    A STUDY OF INTERDIFFUSION OF Pd/Ag BILAYER THIN FILMS BY X-RAY DIFFRACTION STRUCTURE DEPTH PROFILING
    TAO Kun;LI Bin;LUO Jian (Tsinghua University; Beijing 100084)
    Acta Metall Sin, 1997, 33 (7): 742-748. 
    Abstract   PDF (622KB) ( 634 )
    A method has been presented to obtain all X-ray diffraction information, which including the peak intensity, peak position and peak profile, of each layer at different depth respectively. This method can be named as structure depth profiling or computed depth profiling technique of X-ray diffraction (XRD). The samples of Pd(200 nm)/Ag(200 nm) bilayer thin films were used to test this method and to study the interdiffusion in the Pd/Ag system. For sample annealed at 490℃ for 20 min, it was found that there were two solid solutions with different lattice parameter in each layer at different depth. It means that the structure of each layer parallel to the surface is not homogeneous microscopically in the interdiffusion process.
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    MAGNETIC,MAGNETO-OPTICAL PROPERTIES AND THERMAL STABILITY OF Tb/Co MULTILAYER FILMS
    ZOU Zhiqiang;LI Ming;JIANG ZhihonK;LUO Caiqing; SHEN Defang (Shanghai Institute of Metallurgy; Chinese Academy of Sciences; Shanghai 200050)
    Acta Metall Sin, 1997, 33 (7): 749-755. 
    Abstract   PDF (661KB) ( 639 )
    Tb/Co thin films with an artificially layered structure are prepared by a dc magnetron-sputtering system. The form of the compositionally modulated structure is dependent on the deposition rates of Tb and Co targets, and the rotation speed of substrate. The layer-thickness dependence of Kerr rotation hysteresis loops was studied. The results show that the films have large pefpendicular uniaxial anisotropy, large coercivity and large Kerr rotation when the period of Tb/Co film is small. These magnetic properties decrease when the period of Tb/Co film is large. The mechanism can be interpreted in terms of the single-ion anisotropy of Tb ions in the interface, and the ferrimagnetic coupling between Tb and Co atoms. The isothermal annealing of Tb/Co multilayer films at 300 oC shows that it has a bad thermal stability.
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    REACTION BEHAVIOUR OF ZrO_2/Ti INTERFACE IN JOINTING ZIRCONIA CERAMICS AND STAINLESS STEEL 304 WITH Ti FOIL
    WANG Liduo;WANG Yinghua;LI Wenzhi; LI Hengde (Tsinghua University; Beijing 100084); OKI Takeo (Naguya University; Japan)
    Acta Metall Sin, 1997, 33 (7): 756-762. 
    Abstract   PDF (1351KB) ( 567 )
    Reaction behaviour of the interface between ZrO2 and Ti in loining zirconia ceramics and stainless steel with Ti foil as active metal was studied by means of EPMA, XRD, IMA, XPS and AES. The results show that O diffused from the zirconia into the Ti active metal zone to produce TiO. The amount of O in the denaturizing layer was found to decrease. The bonding state of Zr in the denaturizing layer changed from Zr4+ to Zr2+. At the same time, the diffusions of Ti and Zr were found in the zirconia near the interface between zirconia and Ti.
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    RELATIONSHIP BETWEEN VOGELFULCHER LAW AND GLASS TRANSITION TEMPERATURE
    JIANG Qing;XU Xiaoya;ZHAO Ming (Jilin University of Technoloasl; Changchun 130025)
    Acta Metall Sin, 1997, 33 (7): 763-768. 
    Abstract   PDF (524KB) ( 879 )
    The apparent temperatures on Differential Scanning Calorimeter were calibrated by measuring the melting temperature of In, Zn, Sn and Ph with different heating rates, different crucibles and different sample weights. Based on the calibrated results, the kinetic characteristics of the glass transition for Ni33Zr67, Zr65Al7.5Ni10Cu,,Co2.5,Pt69.0Ni9.6P2104, polyethersulfone and polystyrene were studied. The results show that there is a linear relation ship between the logarithm of heating rates and the glass transition temperatures. It is argued that this linear relationship is not against the Vogel-Fulcher law. According to the measured glass transition temperatures and Vogel-Fulcher law, the ideal glass transition temperature and the activation energy for the glass transition were calculated.
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    EFFECTS OF PRESSURE AND TEMPERATURE ON THE MICROSTRUCTURES OF NANOCRYSTALS α-Fe_2O_3
    LI Haibo;CHEN Gang; GONG Jie;HONG Jun;YU Ruihuang (Jilin University; Changchun 130023) (Siping Normal College; Siping 136000)
    Acta Metall Sin, 1997, 33 (7): 769-773. 
    Abstract   PDF (434KB) ( 588 )
    α-Fe2O3 ultrafine particles prepared with precipitation method were treated to form nanocrystals at various presures or temperatures, and their microstructures were studied by means of X-ray and Mbssbauer spectroscopy. The results indicate that high pressure affects mainly the structures of surface of micrograins and interface in nanocrystalline materials.
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    THE INFLUENCE OF DROPLET IMPACT ON METAL INERT GAS WELD POOL GEOMETRY
    WU Chuansong (Shandong University of Technology; Jinan 250061); L. DORN (Berlin Technical University; Germany)
    Acta Metall Sin, 1997, 33 (7): 774-780. 
    Abstract   PDF (1125KB) ( 530 )
    A numerical analysis model for fluid flow and heat transfer in metal inert gas (MIG) weld pools was introduced. It puts emphasis on analyzing how the droplet impact af fects the MIG weld pool geometry, and gives a set of algorithm to calculate weld reinforcement and weld pool geometry. Quantitative analysis is carried out to determine the extent of influence of droplet impact on weld pool geometry when droplet reaches the pool surface. Bead-on-plate MIG welding experiments on mild steel workpieces show that the predicted weld dimensions are in agreement with the measured ones.
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    EFFECT OF INTERFACE PROPERTY ON STRENGTHENING EFFICIENCY OF DUMBBELLSHAPED SHORT-FIBRE REINFORCED COMPOSITE
    SUN Xuekun; QIN Rongshan; LIU Donpoin; ZHO U Benlina (Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015) (International Centre for Materials Physics; Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1997, 33 (7): 781-784. 
    Abstract   PDF (356KB) ( 481 )
    The finite element method was adopted to analyze the dumbbell-shaped and plain short-fibre reinforced composites. Emphasis was put on discussing the effect of interface property on strengthening efficiency of two models. The adaptability of dumbbell-shaped short-fibre model was also studied. The elastic-plastic model was used to make the numerical calculation and one layer of interface element was divided so that the effect of interface property was introduced. From the analysis of steel wire reinforced tin composite, it was revealed that the interface property affects the strengthening efficiency of two models heavily. Especially under the condition of weak bonding interface, the dumbbell-shaped short-fibre model could increase the strengthening efficiency greatly. The analysis method and numerical results could be used as a reference to the design of short-fibre reinforced composites.
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